Pai expects to hold 3 more millimeter wave auctions in the 2nd half of 2019 in the 37GHz, 39GHz, and 47GHz bands. "To help facilitate that auction on this timeline, I’m proposing rules to clean up the 39 GHz band and move incumbents into rationalized license holdings," Pai writes.

The chairman didn't say exactly how much spectrum will be auctioned yet, but the scale and scope of these planned high-band auctions appear to promise to open up the largest tranche of spectrum for wireless broadband yet seen in the US.

In July 2016, the FCC said that it planned to open up 3.85GHz of licensed spectrum in the 28GHz, 37GHz, and 39GHz band. The agency later voted to add 700MHz in the 24GHz band, and nearly 1GHz in the 47GHz band.

The August FCC meeting should further clarify exactly what will be offered in the forthcoming auctions.

One big question that definitely can't be answered yet is whether T-Mobile and Sprint will be allowed to participate in the new auctions, which would likely give them a deal more spectrum build out a 5G spectrum network in 2019 and beyond. T-Mobile said it would like to take part back when it announced the merger in April, but admitted that it didn't know what would be allowed with regard to the 5G auctions.